JP2003110462A - Discriminating method of correlation value - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discriminate a false signal mutual correlation and a weak signal time correlation. SOLUTION: A correlation peak value is detected by a first correlator that detects the correlation peak value in one epoch unit. When the correlation peak value is a weak signal maximum threshold or smaller, the possibility of false signal mutual correlation is determined (203), and a correlation peak value is obtained by a second correlator that detects the correlation peak value in one chip unit (204). When the correlation peak value in one chip unit is a weak signal maximum threshold or larger, the received signal related with the correlation value is considered to be relatively strong and not buried in noises so that it is determined that the correlation peak value depends on the false signal mutual correlation, and the synchronization is not established. When the correlation peak value in chip unit is the weak signal maximum threshold or smaller, the received signal related with the correlation value is considered to be relatively weak and buried in noises so that it is determined that the correlation peak value depends on the weak signal time correlation, and the synchronization is established (205).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectrum corresponding to a transmission source to be acquired and tracked by each transmission source, for example, a positioning satellite, which transmits a spectrum spread signal using a unique spread spectrum code. The present invention relates to a correlation value identification method executed by a receiver in a wireless system such as a positioning system that captures the transmission source by performing code phase synchronization control on a received signal using a despreading code. As an example of such a radio system, a GPS satellite that measures the position, speed, etc. of a GPS satellite in an orbit around the earth as a transmission source and a receiver in a space in which one of the GPS satellites can be seen as a positioning target is measured. Global Pos
itioning System).

[0002]

2. Description of the Related Art In GPS, GP in orbit around the earth
The GPS receiver detects its own position, speed, etc. by the positioning calculation based on the satellite signal received from the S satellite. G
In order to perform the positioning calculation with the PS receiver, it is necessary to select more than the number of GPS satellites required in principle, capture satellite signals from those GPS satellites, and demodulate data from the captured satellite signals. is there. The satellite signal transmitted from the GPS satellite is a signal that is modulated by data of 50 bps indicating the transmission time, detailed orbit information, ephemeris information, etc., and is further spread spectrum by the spread spectrum code determined for each satellite. The GPS receiver despreads the received satellite signal with a spectrum despreading code corresponding to the selected GPS satellite, and demodulates the data from the resulting signal. With a GPS receiver,
Positioning calculation is performed based on the demodulated data of each selected GPS satellite and the code phase obtained as phase control information through spectrum despreading. The spread spectrum code used in GPS is C / A (Coarse).
There are two types, Acquisition code and P (Precision) code, and there are design differences between the two, such as the number of chips per epoch, code speed, and epoch length.
All of them are pseudo-noise codes composed of a predetermined number of chips, and each chip takes a binary value of 1,0. For example,
C / A code is 102 chips per epoch
3, the code rate is 1.023 MHz, and thus the Gold code has a repetition cycle (epoch length) of 1 msec.

Spectrum despreading in a GPS receiver is performed by detecting a correlation value between a spectrum despreading code and a satellite signal, comparing the detected correlation value with a predetermined threshold,
In addition, the phase control of the spectrum despreading code, that is, the code phase control based on the result of this comparison is also involved. First,
The correlation value between the spectrum despread code and the satellite signal is information indicating the degree of matching / mismatch between the value of the pseudo noise code related to the satellite signal and the value of the spectrum despread code. When the value and the value of the spectrum despreading code are the same over the entire epoch, that is, when the chip position of the spectrum despreading code, that is, the code phase, is synchronized with the satellite signal, compared to other states. Noticeably larger. Therefore, in the GPS receiver, the detected correlation value is compared with the threshold value, and when the former exceeds the latter, it is determined that "the code phase is synchronized". It should be noted that this threshold is set in advance so that the code phase synchronization state can be detected separately from other states. In the GPS receiver, while shifting the code phase of the spectrum despreading code by, for example, one chip until the code phase is synchronized, that is, until the satellite signal is captured, and the entire one epoch is checked, Perform correlation value detection and threshold comparison. When the code phase was shifted over one epoch and examined, but if the judgment of "synchronization" cannot be obtained, the local oscillation frequency may be slightly shifted because it may not be frequency synchronized with the carrier of the satellite signal. try again. In the code phase locked state, it is possible to despread the satellite signal and demodulate the data, and at the same time, the code phase at that time, that is, the code phase at which the correlation value reaches a peak, can be used for deriving the pseudorange. After capturing the satellite signal once, the satellite (signal) is tracked by changing the code phase so as to follow the phase change of the pseudo noise code related to the satellite signal.

[0004]

However, in order to always correctly establish the code phase synchronization of the spectrum despread code with respect to the received signal (satellite signal in the case of GPS), the method of simply comparing the correlation value with the threshold is not enough. This is because (1) a weak correlation value, that is, a false signal cross-correlation value generated for a reception signal from a transmission source (satellite in the case of GPS) different from the transmission source corresponding to the spectrum despreading code, and (2) the correlation value Weak correlation values that occur at phases other than the peak code phase, that is, false position autocorrelation values, (3) Correlation with the transmission source and the code phase are correct, but the correlation level of the correlator is low. This is because the signal correlation value and the like cannot be identified by a simple threshold comparison.

First, considering the C / A code in GPS as an example, there is no distortion in the satellite signal waveform, and the input level of the received satellite signal to the correlator is, for example, -110 dB.
When the spectrum despreading code corresponding to the transmission source of the satellite signal is used and the spectrum despreading code is accurately code-phase-synchronized with the satellite signal under the quasi-ideal situation with a high ratio of about m. The number of matching chips per epoch is 1023. When the absolute value of the difference between the number of matching chips and the number of non-matching chips is referred to as a correlation value, it can be said that the correlation value in this case, that is, the strong signal correlation value is 1023. However, since the actual satellite signal waveform is distorted, the strong signal correlation value is lower than this ideal value, for example, about 1023 × 40.0% = 409.2.

Next, the satellite signal reception level is further increased to 23.7.
If it is lower by dB and −133.7 dBm, then 23.7 dB =
As can be read from the equation of −20 × log (2.6 / 40.0), the correlation value, that is, the correlation value at the time of weak signal is 1023 × 2.
6% = 26.2.

On the other hand, if the satellite signal reception level is sufficiently high, the false signal cross-correlation value may be approximately the same as the above weak signal correlation value. That is, in GPS, different GPS
Since the correlation value between the C / A codes related to the satellite may increase up to 33, if the signal strength and distortion are similar to those at the time of the strong signal, the false signal cross-correlation value is 33 at maximum. × 40.0% = 26.0 can be obtained. This false signal cross-correlation value is almost equal to the weak signal correlation value due to the satellite signal having a level lower than that of the strong signal by 23.7 dB, that is, 26.2 described above.

As described above, the weak signal correlation value and the false signal cross-correlation value can be close to each other, and the latter may be larger depending on the radio wave environment. Therefore, the correlation value at the time of weak signal is definitely judged as "synchronous" and the false signal cross-correlation value is "asynchronous"
It is difficult to set the threshold so that it can be judged. As a result, in the past, the risk of determining "code phase = asynchronous" based on the weak signal correlation value and the risk of determining "code phase = synchronization" based on the false signal cross-correlation value was considered in the receiver design. It was included. A similar problem occurs between the weak signal correlation value and the false position autocorrelation value.

The present invention has been made to solve the above problems, and a signal spread spectrum is transmitted by a different spread spectrum code for each transmission source, and a predetermined number of transmission signals are transmitted to a receiver. In a wireless system in which the source is selected and the received signal is despread by the corresponding spectrum despreading code, the weak signal correlation value and false signal cross-correlation value (and false position autocorrelation value) appearing in the correlation detection value at the receiver ) And so that they can be identified more reliably.

[0010]

In order to achieve such an object, the correlation value identifying method according to the present invention is as follows. (1) Each transmission source transmits a spectrum spread signal using its own spread spectrum code. Executed by the receiver in a wireless system that transmits and then captures the transmission source by performing code phase synchronization control on the received signal using the spectrum despreading code corresponding to the transmission source to be acquired and tracked (2) The correlation value of the spectrum despreading code with respect to the received signal is detected using one epoch of the spectrum despreading code or a large number of chips as a repeating unit, and the detected correlation value exceeds the first criterion. When the signal is shown, the received signal is a strong signal and the spectrum despreading code corresponding to the source of the received signal is used. First separation step of starting the operation of tracking the transmission source by using the spectrum despreading code, and (3) the correlation value detected in the first separation step is the first criterion. When the correlation is below 1, the correlation value of the spectrum despreading code with respect to the received signal is detected by using one chip of the same spectrum despreading code or a small number of series chips as a repeating unit,
When the detected correlation value shows a correlation exceeding the second criterion, it is determined that the received signal is a strong signal and the spectrum despreading code corresponding to the transmission source which is the transmission source of the received signal is not used. Then, while prohibiting the operation of tracking the transmission source by using the spectrum despreading code, when the detected correlation value shows a correlation lower than the second reference, the transmission source which is the transmission source of the reception signal A second demultiplexing step for deciding that the received signal is a weak signal, even though the spectrum despreading code corresponding to is used, and starting the operation of tracking the transmission source using the spectrum despreading code. It is characterized by having. The correlation value identifying method according to the invention is also (1) each transmission source transmits a spectrum-spread signal using a unique spread spectrum code, and the receiver has a spectrum corresponding to the transmission source to be acquired and tracked. This is executed by the receiver in a radio system that captures the transmission source by performing code phase synchronization control on the received signal using the despread code, and (2) 1 of the spectrum despread code.
Detecting the first correlation value of the spectrum despreading code with respect to the received signal by using an epoch or a large number of series of chips as a repeating unit, and (3) repeating one chip or a small number of chips of the spectrum despreading code. Detecting the second correlation value of the spectrum despreading code for the received signal as a unit, and (4) determining the reference range of the second correlation value based on the first correlation value,
(5) a step of determining whether or not the second correlation value belongs to the reference range, and (6) a strong signal correlation when the second correlation value is within the reference range as a result of the determination. Or weak signal time correlation, otherwise regarded as false signal cross-correlation, in the case of strong signal time correlation or weak signal time correlation, start the operation of tracking the transmission source using the spectrum despread code, In the case of false signal cross-correlation, the step of prohibiting the shift to the tracking operation is included. In the present invention, for example, each positioning satellite as a transmission source is
Positioning is performed by transmitting a spectrum-spread signal using a unique spread-spectrum code, and the receiver performing code phase synchronization control on the received signal using the spectrum despreading code corresponding to the positioning satellite to be acquired and tracked. Performed by the receiver in a positioning system that captures satellites.

As described above, in the present invention, the strong signal time correlation is identified based on the correlation value in units of one epoch or a large number of chips, and the strong signal time correlation is recognized, while one chip or a small number of chips are taken as a unit. The weak signal correlation or the false signal cross-correlation is discriminated based on the correlation value. Alternatively, a reference range is determined based on a correlation value in units of 1 epoch or a large number of chips, and determination is performed based on this reference range with respect to a correlation value in units of 1 chip or a small number of chips. Identifying false signal cross correlations to correlations. Therefore, it is possible to shift to transmission source tracking only in the case of strong signal time correlation and weak signal time correlation, and execute processing such as acquisition retry in the case of false signal cross correlation.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

(1) Overall Function and Operation FIG. 1 shows a schematic functional configuration of a GPS receiver according to an embodiment of the present invention. In the receiver shown in this figure, the satellite signal is received by the antenna 101, and the frequency conversion unit 10
2, down-converted, sampled by the A / D converter 103, and input to the correlators 104 and 120. The correlators 104 and 120 and the signal generator 105 are
Depending on the number of satellites required for positioning calculation, the number of chips per epoch of the spread spectrum code related to the satellite signals to be captured / tracked, and the allowable device size / cost, etc.
A plurality of I, Q phases are provided and operated in parallel or sequentially. The reception control unit 106
Correlator 1 according to the information from position / speed calculator 112
Based on the outputs of 04 and 120, the operation of the signal generator 105, particularly the frequency of the local oscillation signal to be generated, the type of spectrum despread code (pseudo noise code) to be generated, the code phase of each spectrum despread code to be generated, etc. Control.

The correlator 104, the reception control unit 106 and the signal generator ("pseudo noise code and local oscillation signal generator" in the figure) 105 constitute a synchronous loop for satellite signals with respect to both carrier frequency and code phase. ing. Correlator 120, reception control unit 106, and signal generator 105
Forms a loop that provides correlation value information that reinforces the correlation value information obtained from this synchronization loop. Correlator 1
04 is an epoch (1 cycle of spread spectrum code = C / A
The correlator 120 detects the correlation value on a chip basis in 1023 chips). The correlator 104 is a member related to normal acquisition / tracking operation, and the correlator 120 is a member related to weak signal separation processing. As will be described later, the characteristic processing in this embodiment is weak signal separation processing using the correlator 120.

First, the reception control unit 106 causes the signal generator 105 to generate a spectrum despread code corresponding to each satellite belonging to the combination selected by the position / velocity calculation unit 112, and the code phase thereof to the correlator 104. The correlation value that is the output of is controlled to be the peak value (correlation peak value) (“capture”). By this control, the code phase synchronization of the spectrum despreading code with respect to the satellite signal is established,
Therefore, when the satellite signal is despread in spectrum, the data demodulation unit 110 can demodulate data from the satellite signal. The demodulated data, for example, detailed orbit information of the transmission source satellite and data relating to the transmission time are supplied to the position / speed calculation unit 112. Reception control unit 106
Controls the code phase in the signal generator 105 (“tracking”) based on the correlation value obtained successively so that this state, that is, the code phase synchronization state is maintained. As such, the loop including the correlator 104 is a code phase locked loop, while the loop including the correlator 120 provides correlation value information for discriminating the false signal cross-correlation value and the weak signal correlation value. This is a loop (described later).

In a member (or frequency converter 102) (not shown) before the input stage of the correlators 104 and 120, the satellite signal is converted to a lower frequency by the local oscillation signal supplied from the signal generator 105. It The satellite signal for which the code phase synchronization is established is the satellite signal after this frequency conversion. Here, the signal generator 105
If the local oscillating frequency at is deviated, even if the code phase synchronization is once established, the synchronization easily deviates with the passage of time. Therefore, it is not possible to track the satellite signal only by the operation as the code phase locked loop described above. Can not. The reception control unit 106 shifts the code phase over one epoch of the spectrum despreading code and examines it. However, when the code phase synchronization cannot be established, the local oscillation frequency in the signal generator 105 is slightly adjusted, and the correlation value is adjusted. The local oscillation frequency control is performed based on to synchronize the local oscillation frequency with the carrier frequency of the satellite signal (carrier frequency synchronization loop).

In a state where both carrier frequency synchronization and code phase synchronization with respect to the satellite signal are established, that is, in the state where the spectrum-despread satellite signal is obtained via the correlator 104, the reception controller 106 causes the correlator 104 to operate. Data demodulation unit 1
10 and demodulates data such as detailed orbit information, while the signal generator 1 out of the information obtained through synchronization control.
The code phase in 05 is given to the pseudo distance measuring unit 109 and the pseudo velocity measuring unit 108, and the local oscillation signal frequency in the signal generator 105 is given to the Doppler frequency measuring unit 111. The pseudo distance measuring unit 109 obtains a pseudo distance to the transmission source of the satellite signal, that is, a code pseudo distance based on the code phase. The pseudo speed measuring unit 108 detects the time change of the code phase and obtains the moving speed of the receiver with respect to the transmission source of the satellite signal, that is, the pseudo speed. The Doppler frequency measuring unit 111 obtains the Doppler shift of the satellite signal carrier frequency, and thus the moving speed of the receiver with respect to the transmission source, that is, the Doppler speed, from the change of the local oscillation frequency.

The position / velocity calculation unit 112 calculates the position of the receiver using the code pseudo distance obtained by the pseudo distance measurement unit 109 in addition to the data demodulated by the data demodulation unit 110. In addition, the position / speed calculation unit 112
Calculates the moving speed of the receiver with respect to the earth surface or the center based on the pseudo speed obtained by the pseudo speed measuring unit 108 and the measurement result by the Doppler frequency measuring unit 111. The position / speed calculation unit 112 notifies the user of the calculation result and the like via a display device, a voice output device, a communication line, etc., which are not shown. The position / velocity calculation unit 112 further selects and selects a combination of satellites used for positioning based on the information demodulated by the data demodulation unit 110, the information acquired and calculated in the past, and the like. The reception control unit 106 is instructed to receive (capture / track) satellite signals from GPS satellites.

(2) Countermeasure against False Signal Cross Correlation In FIG. 2, among the procedures executed by the reception control unit 106 in this embodiment, the false signal cross correlation and the weak signal correlation are distinguished and separated. The flow of the weak signal separation procedure for is shown.
As shown in this figure, the reception control unit 106 first inputs a correlation value from the correlator 104 (201) and compares the input correlation value with the weak signal minimum threshold (202). The weak signal minimum threshold is set to a sufficiently small value, and if the correlation value is below the weak signal minimum threshold, the current code phase (code chip) cannot establish the code phase synchronization of the spectrum despreading code with respect to the received signal. Can be seen. Therefore, when such a result is obtained in step 202, reception control section 106 appropriately changes the code phase of the spectrum despread code in signal generator 105, and returns to step 201 to continue the processing.

When a result that the correlation value is equal to or more than the weak signal minimum threshold is obtained in step 202, the correlation value is a correlation peak due to the weak signal correlation, the strong signal cross correlation or the false signal cross correlation. May be a value.
The reception control unit 106 determines that such a result is Step 202.
If obtained, the correlation value is first compared with the weak signal maximum threshold (203). The weak signal maximum threshold is set larger than the maximum correlation value obtained by weak signal time correlation or false signal cross-correlation.If the correlation value exceeds the weak signal maximum threshold, the correlation value is a strong signal correlation value. Can be considered to be Reception control unit 10
If the correlation value exceeds the weak signal maximum threshold value as a result of the comparison in step 203, 6 determines that the correlation value is a strong signal correlation value, and relates to the correlation value. In order to track the satellite, the procedure shifts to a tracking (not shown).

The reception control section 106 has the correlator 104 to 1
In parallel with obtaining the correlation value in epoch units, the correlator 12
The correlation value in units of 0 to 1 is obtained and stored for 1023 chips, for example. Although not shown, a storage circuit for that purpose may be provided inside the reception control unit 106, or may be provided outside so that it can be provided to the position / speed calculation unit 112 and the like. Further, it is not necessary to store 1023 chips, that is, one epoch, as long as the number of chips occupying a significant ratio with respect to 1023 chips can be stored. The correlation value stored in this way for each chip is the reception control unit 106 when the result that the correlation value is less than or equal to the weak signal maximum threshold is obtained in step 203.
(204).

The reception control unit 106 relates to the satellite found in step 203 that the correlation value in 1-epoch units is less than or equal to the weak signal maximum threshold, and stores the correlation value in 1-chip units for, for example, 1023 chips. The one having a representative value (for example, average value, upper 3/4 value, maximum value, etc.) among the read correlation values is compared with the weak signal maximum threshold (205). The weak signal maximum threshold in step 205 is also a threshold set to be larger than the maximum correlation value obtained by weak signal time correlation or false signal cross-correlation.
The comparison target in 02 is the correlation value in 1 epoch unit, whereas the comparison target in step 205 is the correlation value in 1 chip unit, and the scale (the number of sampling points)
, The weak signal maximum threshold values in steps 202 and 205 are different from each other.

As a result of the comparison in step 205, when it is found that the representative value of the correlation values extracted in step 204 is less than or equal to the weak signal maximum threshold, the reception control unit 106 inputs from the correlator 104 in step 201. The correlation value thus determined is considered to be due to the weak signal correlation, and the tracking procedure is started to track the satellite associated with the correlation value. On the other hand, when it is determined that the maximum weak signal threshold is exceeded, the reception control unit 106 determines that the correlation value input from the correlator 104 in step 201 is due to the false signal cross-correlation, and proceeds to step 201. Return.

As described above, in this embodiment, the correlator 10
Of the correlation values (201) in 1 epoch unit obtained in 4 above, those that can be recognized as the correlation peak value (202) and that are not due to the strong signal correlation (203) ), Based on the representative value (204) of the correlation value for each chip obtained by the correlator 120, it is determined whether it is due to the weak signal time correlation or the false signal cross correlation (205). . 1
We can distinguish the weak signal time correlation and the false signal cross-correlation by the representative value of the correlation value on a chip basis.As described below, the weak signal is usually buried in noise and the spectrum received signal waveform is corrupted. On the other hand, if the signal is strong enough to cause the false signal cross-correlation, the received signal waveform is not so distorted.

First, the signals transmitted from GPS satellites are
Since this is a signal in which a carrier of a predetermined frequency is modulated according to the data to be carried and further spread spectrum is spread according to a predetermined spread spectrum code, the modulation component includes the data modulation component and the spread spectrum modulation component.
Since the signal / satellite acquisition by the GPS receiver is achieved through the phase synchronization of the spread spectrum despreading code with respect to the spread spectrum modulation, the spread spectrum modulation in the signal "clearly" remains as it is when it is transmitted from the satellite. If saved, the GPS receiver would be able to accurately capture the signal / satellite.

However, in reality, the signal transmitted from the GPS satellite traces a long radio propagation path from the orbit around the earth to the GPS receiver before reaching the GPS receiver, and therefore is significantly attenuated. In addition, refraction and phase shift due to ionosphere and other propagation obstacles / layers, and Doppler shift due to relative movement of GPS satellite-to-GPS receiver also occur. Therefore, GP
The received signal in the S receiver, especially its spread spectrum modulation component, does not maintain the "clean" modulation waveform as it was at the time of transmission. As a general trend, the stronger the received signal follows the better radio propagation path, the better the modulation waveform is preserved, while the weaker received signal follows the poorer radio propagation path, which is buried in noise and modulated. It can be said that the waveform is broken.

Therefore, it can be said that the spread spectrum modulation component can be detected as "clear" from a strong signal, whereas only the "blurred" can be detected from a weak signal.
In other words, if the spread spectrum modulation component could be detected as "clear" from the received signal that produced a correlation peak value that was about the time of weak signal correlation, the correlation peak value would actually be due to the false signal cross-correlation. On the contrary, if only spread spectrum modulation could be detected as "blurred" from the received signal that produces a correlation peak value that is approximately that of a weak signal, the correlation peak value is certainly due to the weak signal correlation. Will.

In the present embodiment, in order to discriminate whether the spread spectrum modulation component appears "clearly" or only "bluntly" in the received signal,
The correlator 120 detects the correlation value for each chip. Here, the correlation value in one epoch unit obtained by the correlator 104 is a correlation value obtained by sampling over the entire one epoch (= 1023 chips (in the case of C / A code)). Then, the correlation value in the unit of one chip obtained by the correlator 120 is a correlation value obtained by sampling only one chip (not necessarily one if the number is sufficiently small). The correlation value in one epoch unit is small, but the representative value of the correlation value in one chip unit is large, which means that the received signal itself is a strong signal and the modulation waveform at the time of transmission is "clear". , The correlation value per epoch is small due to the false signal cross-correlation. On the contrary, both the correlation value in 1 epoch unit and the representative value of the correlation value in 1 chip unit are small, which means that the received signal itself is a weak signal and the modulated waveform at the time of transmission is “blurred”.
It means that the correlation value in one epoch unit is small because it is only stopped. The weak signal separation procedure in this embodiment, particularly steps 204 and 205, is a process that utilizes this.

For example, the number of sampling points per chip in the correlator 120 is set to "clear" or "blunt".
It is assumed that the number is set to be sufficiently large, for example, 8 points so that they can be identified. In this case, the number of sampling points at which the spread spectrum modulation component of the received signal and the spread spectrum despread code value match, that is, the correlation value in 1-chip units is, for example,

## EQU1 ## It is assumed that the values are 1st chip = 8, 2nd chip = 8, 3rd chip = 0, 4th chip = 8, .... The difference between these values and the virtual average is calculated with the virtual average being 4, and the average value of the absolute values is calculated to be 4. Further, it can be seen that the correlation value is greatly changed when comparing the chips. On the contrary,
The correlation value in 1-chip units is, for example,

## EQU00002 ## It is assumed that the values of the first chip = 6, the second chip = 6, the third chip = 5, the fourth chip = 6 ,. When the difference between these values and the virtual average is calculated with the virtual average being 4, the average value of the absolute values thereof is 1.78, and there is no large difference in correlation value between chips.

Such a difference in properties, that is, a difference in the difference between the chips and the correlation value between the chips cannot be known from the correlation value in one epoch unit. Even if multi-point sampling is performed for each chip when detecting the correlation value in one epoch unit, the magnitude of the correlation value in each chip cannot be known as long as the correlation value in one epoch unit is obtained.
In this embodiment, the weak signal maximum threshold is set to 7
Since step 205 is executed as described above, the “clear” condition, that is, the false signal cross-correlation shown in Formula 1 and the “blunt” condition, that is, the weak signal time correlation shown in Formula 2, can be identified.

In the above embodiment, step 20
If it is not determined that the maximum signal is less than or equal to the maximum threshold of the weak signal in step 3, the determination in step 205 is not performed, but the process related to the correlation value in one epoch unit and the process related to the correlation value in one chip unit are performed. It does not matter whether it is always performed regardless of the correlation value in one epoch unit.
That is, when the correct spectrum despreading code corresponding to the transmission source satellite is used, the correlation value in one epoch unit changes according to the received signal strength. Therefore, it is possible to estimate the range Lmin to Lmax of the received signal strength where the correlation value is obtained from the correlation value in one epoch unit.
Furthermore, the received signal strength range Lmin-
From Lmax, the received signal strength range Lmin to Lma
Correlation values Cmin to Cm in 1-chip units obtained when a signal having an intensity belonging to x is received and correlation detection is performed using a correct spectrum despreading code corresponding to the transmission source satellite.
The range of ax can be estimated. For weak signal correlation and strong signal correlation, the correlation value for each chip is
Correlation value range Cmin to Cma in 1 chip units corresponding to the signal strength range estimated from the correlation value in 1 epoch units
It becomes a value belonging to x. On the other hand, the correlation value obtained when performing the correlation detection using the spectrum despreading code that does not correspond to the transmitting satellite, that is, the false signal cross-correlation value, as can be inferred from the principle described above, The correlation value in 1-chip unit is a value that greatly exceeds the range Cmin to Cmax corresponding to the signal intensity range estimated from the correlation value in 1-epoch unit. Therefore, when carrying out the present invention, the correlation value is detected in units of one epoch and the reference range C
min-Cmax is determined, the correlation value is detected in 1-chip units, and the correlation value is set in the reference range Cmin-Cmax.
If the result of the judgment is "within the reference range", the correlation with strong signal or weak signal, "outside the reference range"
It is also possible to employ an embodiment in which the false signal cross-correlation is obtained if the determination result of is obtained. In order to distinguish the strong signal correlation and the weak signal correlation, threshold value determination may be performed on the correlation value in units of one epoch or one chip.

(3) Addendum Regarding false position autocorrelation value and weak signal correlation value, all chips (1023 in C / A code) belonging to one epoch are added.
By detecting the correlation value for
It is possible to discriminate between the 023 different code phases by checking the correlation values and selecting the code phase showing the maximum correlation value and having a sufficiently large correlation value among them. This process is sufficient if the correlation value is less than or equal to the weak signal maximum threshold and is not the false signal cross-correlation, and therefore the process shown in FIG. 2 is performed before the reception process (= tracking process).

The present invention is not limited to the C / A code, but can be applied to the P code in principle. The present invention can be applied to a GPS receiver having various reinforcements or modifications, for example, a GPS receiver having a DGPS function. Further, not only the GPS receiver, but also a receiver that receives a spread spectrum signal by selectively using a plurality of types of spread spectrum codes, especially a receiver whose reception level may be extremely low The invention can be applied. The present invention has a large number of chips per epoch,
The effect becomes remarkable when it is applied to the one in which the false signal cross-correlation value is relatively large, the one in which the transmitter and the receiver are asynchronous, and the like.

In addition, the applicant of the present application filed Japanese Patent Application No. 2000-34.
In 3056, a method of changing a threshold for determining a correlation value by following the result of the correlation value determination is proposed. Although this method can also deal with a part of the trouble caused by the weak signal, the present invention is superior in terms of speed and reliability. That is, in the present invention, since the false signal cross-correlation value and the weak signal correlation value can be discriminated without using the positioning result regarding the position of the receiver, the false signal cross correlation value at the time before the positioning result to be used is obtained. The influence of the correlation value can be prevented.

[Brief description of drawings]

FIG. 1 is a block diagram showing a functional configuration of a GPS receiver according to an embodiment of the present invention.

FIG. 2 is a flowchart showing an example of a weak signal separation procedure according to this embodiment.

[Explanation of symbols]

101 antenna, 104, 120 correlator, 105
Pseudo-noise code and local oscillation signal generator, 106 reception control unit, 111 Doppler frequency measurement unit, 112 position / speed calculation unit.

Claims (3)

[Claims] 1. Each transmission source transmits a signal that has been spread spectrum using a unique spread spectrum code,
A radio system in which the receiver acquires the transmission source by performing code phase synchronization control on the received signal using the spectrum despreading code corresponding to the transmission source to be acquired and tracked. The correlation value of the spectrum despreading code with respect to the received signal is detected using one epoch of the despreading code or a large number of series of chips as a repeating unit, and when the detected correlation value shows a correlation exceeding the first criterion, It is determined that the received signal is a strong signal and that the spectrum despreading code corresponding to the transmission source that is the source of the reception signal is used, and the transmission source is tracked using the spectrum despreading code. The first separation step to be started and the correlation value detected in the first separation step indicate a correlation lower than the first criterion. In addition, the correlation value of the spectrum despreading code with respect to the received signal is detected by using one chip or a small number of series chips of the same spectrum despreading code as a repeating unit, and the detected correlation value shows a correlation exceeding the second criterion. If the received signal is a strong signal and it is determined that the spectrum despreading code corresponding to the transmission source that is the source of the received signal is not used,
While prohibiting the operation of tracking the transmission source by using the spectrum despreading code, when the detected correlation value shows a correlation lower than the second reference, it corresponds to the transmission source which is the transmission source of the reception signal. A second demultiplexing step for starting the operation of tracking the transmission source by using the spectrum despreading code, while judging that the received signal is a weak signal although the spectrum despreading code is used. A method for identifying a characteristic correlation value. 2. Each transmission source transmits a signal spread spectrum using its own spread spectrum code,
A radio system in which the receiver acquires the transmission source by performing code phase synchronization control on the received signal using the spectrum despreading code corresponding to the transmission source to be acquired and tracked. The step of detecting the first correlation value of the spectrum despreading code with respect to the received signal using one epoch of the despreading code or a large number of series of chips as a repeating unit, Detecting a second correlation value of the spectrum despreading code for the received signal as a unit of repetition; determining a reference range of the second correlation value based on the first correlation value; As a result of the above determination, if the second correlation value is within the reference range. Is considered as strong signal time correlation or weak signal time correlation, otherwise it is considered as false signal cross correlation, and when strong signal time correlation or weak signal time correlation, the transmission source is tracked using its spectrum despread code. And a step of prohibiting the transition to the tracking operation in the case of false signal cross-correlation, the correlation value identifying method. 3. The correlation value identifying method according to claim 1, wherein each positioning satellite that is a transmission source transmits a signal that is spread spectrum using a unique spread spectrum code, and a receiver acquires and A correlation value characterized by being executed by the receiver in a positioning system that captures the positioning satellite by performing code phase synchronization control on the received signal using the spectrum despreading code corresponding to the positioning satellite to be tracked. Identification method.